This pilot clinical study evaluates a new paradigm of harnessing dendritic cells (DC) to initiate tumor immunity by using in vivo gene transfer to activate endogenous DC in tumors, circumventing the necessity of ex vivo manipulation to activate DC. Based on extensive pre-clinical data, this study will evaluate the concept that transient modification of the genetic repertoire of esophageal tumors to express CD40 Ligand (CD40L; a potent activator of DC) will induce the accumulation of activated DC within the tumor, and the in vivo interaction of DC with the tumor cells/tumor antigens will induce tumor-specific immunity. To assess this concept, an adenovirus (Ad) vector (AdCUCD40L) will be used to transfer and transiently express the human CD40L cDNA in esophageal carcinoma by endoscopic, intratumoral administration. The specific aims of the study include: (1) to determine if it is safe to administer the AdCUCD40L vector to esophageal tumors; (2) to evaluate the hypothesis that intratumoral administration of the AdCUCD40L vector will result in the accumulation in the tumor and in regional lymph nodes activated DC and other relevant immune cells, and the induction of tumor-specific immunity; and, (3) to determine if changes in glucose uptake by tumors as measured by [18F] 2-Fluoro 2-deoxyglucose positron emission tomography (FDG-PET) will correlate with antitumor immune responses. The study will be carried out in two phases. First, individuals in part A (n=12) with unresectable stage III or IV esophageal cancer will be used to assess safety/toxicity with ascending doses of the AdCUCD40L vector. Second, once the safety profile is determined, part B (n=30) will assess the administration of the highest non-toxic dose of the AdCUCD40L vector (or control vector, or a placebo, in a randomized, blinded fashion) to resectable, stage I-III esophageal cancer 5 or 15 days prior to surgery. Patients in both parts will be evaluated with FDG-PET both before and after vector administration at defined timepoints. The tumor, regional/distant nodes removed at surgery, and peripheral blood will be assessed for the numbers and state of activation of DC and relevant immune cells, levels of expression of genes coding for relevant immune mediators, and the presence of tumor-specific immunity. This study will help determine if intratumoral administration of the AdCUCD40L vector is safe, and evokes sufficient DC-related host responses to warrant further studies in esophageal cancer.